1. Field of the Invention
The present invention relates to a method for manufacturing ceramic powder, and ceramic powder and composite material.
2. Description of Related Art
Fine ceramic powder can be obtained by mixing raw materials, calcinating the mixed raw materials after drying, and crushing them with a crusher like a ball mill or the like. Then, after drying the resultant substance with a spray drier, the substance is processed through a crusher such as a pneumatic crusher to obtain ceramic fine powder.
While these ceramic powders can be used on its own, they are also used as composite material dispersed within resin materials. The requirements for ceramic powders to be used as composite materials are that the powders must have dispersant and filler properties against resin materials. The particle size of particles composed of the powder is one of the factors for securing dispersant and filler properties against resin materials. For example, in addition to the method explained above, ceramic powder can be manufactured from liquid phase state like the co-precipitation method. However, the particle sizes of these powders are so small that it is impossible to secure the dispersing and filler properties against resin materials. Also, the particles in ceramic powder obtained under the method described above come in irregular shape because they are obtained through pulverizing. Thus, the dispersant and filler properties required for resin materials cannot be secured under this method.
Several techniques for manufacturing spherical shaped ceramic powder have been proposed in the past. In one of the conventional techniques, inorganic powder suspended in a flammable gas is sprayed into burning flames to heat and form the inorganic powder into spherical particles. In this method, the inorganic powder is sprayed at a spray speed of 70 to 1,200 m/sec from the tip of the burner nozzle. In one practical example using this technique, silica (SiO2) powder having a mean particle size of 0.5-30 μm can be obtained.
By another technique, a proper binder is kneaded with ceramics having biological absorbability to prepare a slurry and this slurry is dripped on a high temperature heating body. The slurry is dried on the high temperature heating body while being formed into a spherical shape and subsequently sintered at high temperature to obtain spherical ceramics.
In another technique, ceramic fine formed spherical particles are produced through forming ceramic powder obtained by a stirring granulation method. When such particles are produced, granules of ceramic powder obtained by a spray drying method are used as nuclei.
The techniques explained above entail some difficulties. For example, in the first technique that uses flammable gas, it is difficult to control the environment and temperature because flammable gas is directly sprayed (on the material). Because of this, it would be difficult to obtain ceramic powder with multiple ingredients like composite oxides.
In the second technique in which slurry is dripped on a high temperature heating body, although obtained powder particles are generally spherical, they are large in diameters ranging from 0.3 to 1.2 mm (300 to 1,200 μm), which are unsuitable for being used as composite material with resin.
The third technique is aimed at providing particles with particle sizes ranging from 0.02 to 0.4 mm (20 to 400 μm), which are also unsuitable to be used as composite material with resin material.
One prior art describes an injection mold material containing binder resin and spherical ceramic powder with a mean particle size of less than 7 μm, without teaching any specific methods for obtaining such spherical ceramic powder.
As noted above, it was difficult by the conventional methods to obtain powder with spherical particles having appropriate particle sizes for creating composite materials with resin.
Notably, no method has yet been devised to obtain multi-ingredient ceramics of the composite oxide type.